Tag Archives: Mile-a-Minute Vine (Mikania micrantha) is pondering the possibility of over-running Florida from a start in Miami. Why has it remained localized so far? Trying to figure out ferns are truly native is

What did Charles Darwin do after rocking the world with evolution? The aftermath was a little anticlimactic, like a retired CEO heading the homeowners association. One thing Darwin did was study climbing vines, and one of his climbers was Mikania scandens. He queried through international correspondence if Mikania scandens always twines in the same direction as it climbs. Darwin sent letters on sailing ships. I used Google Images, and every Mikania I see there cranks counter-clockwise. (Would they go clockwise below the equator? (Just kidding.) ((I think.))

Mikania scandens wrapping counter-clockwise. By John Bradford.

John and I rocked the world today working on insects and frogs in Savannas State Park near Jensen Beach, FL, a perfect place to trip over Mikania scandens.

Florida has three species of Mikania: Mikania scandens, the similar M. cordata, and the reason I’m mentioning the trio: The exotic invasive Mikania micrantha is called Mile-a-Minute Vine growing 60 MPH and blanketing acres in the wink of an eye. Good thing it is, I hope, sprawling only across the Miami-Dade Area. But all things do have their good points, and a smothering rampant vine is just what you need if you have something to hide Camouflage is how it served during WWII, the military helping to spread it around the tropical world. War has odd ramifications, such as that (dud) hand grenade a bicyclist stumbled upon, almost literally, recently trailside in Jonathan Dickinson State Park, aka WWII Camp Murphy.

Mikania cordifolia in fruit. By JB

Our bio-peek today is about hand grenades, tiny ones, if the story that follows bears scrutiny. Please know that the tale resembles the prosecutor’s case…made-up to account for the facts as we know them. Innocents have gone to the chair on occasion.

First a little background. In the Aster Family, where Mikania belongs, the flowers are crowded into dense clusters called heads. The flower bases are packed together side-by-side vertically like stems in a vase. Each base matures into a fruit similar to a seed, so let’s just wink and call it a seed (if you prefer, call it an achene). Packed with sugars and starch, seeds are good to eat.

Diagram of an Aster Family flower head. The flower bases (ovaries in the caption, blue) are packed together vertically and become the “seeds.” In real life they are jammed together, not separated as in the diagram.

Seed pests are a pervasive torment for members of the Aster Family. Little troublemakers, often tiny maggots, nestle down among the maturing “seeds” and damage them by nibbling.

The crowd calls out DE-FENSE, DE-FENSE. Here come those micro hand grenades…packed in among the seeds. Under a microscope little hard grainy translucent spheres cover the seeds. The little death bombs (if my speculative interpretion of their purpose is correct) are a handbook recognition feature for Mikania scandens. (M. micrantha can have some as well.)

“Seed” (achene) removed from the flower head covered with what I think are anti-maggot death bombs. The white material to the lower right is a parachute…think of a dandelion for familiar related species with parachute seeds.

A loathsome larva has to nibble and wriggle past the tiny spheres to get to the tasty seedflesh. They break loose easily and perhaps even stick to the pest infusing it transdermally with toxins like “the patch.”

Defensive weapons need some zip, and our species has plenty to give although I don’t really know if the seed-covering gems contain the secret sauce. That sauce is beyond toxic. Its diverse ingredients include a wicked compound named for the plant, mikanolide. It (and maybe its associates) block the enzyme DNA polymerase. That may sound harmless without a reminder of its necessity in forming DNA, the genes, the info center for every living cell. Nuking the DNA would be the same as yanking the motherboard from my laptop on my lap. Poisons don’t get much more direct or universal than that.

So clearly Mikania has the right stuff to destroy ANY living cell, whether it be a seed-munching larva or a malignant human tumor. (Please do not eat the weeds.) Tilted more toward that tumor, mikanolide-based therapy has made it to the U.S. Patent Office.